The following information is offered solely to assist the understanding of the reader, and none of the information is admitted to describe or constitute prior art to the claims of the present invention.
The process of filtration is necessary to remove undesirable substances from liquids. Such substances can exist in a variety of forms, ranging from large, insoluble material to small, soluble organic or inorganic molecules. Accordingly, each form presents a different challenge to the task of filtration. Complexities arise when several forms of unwanted substances are present in the same liquid solution, i.e. both large and small, soluble and insoluble, particulate and non-particulate, organic and inorganic, etc. Liquids that are uniform in composition are therefore easier to filter, while those with more complex constructions can be more difficult.
This problem becomes particularly evident when a liquid containing insoluble material is filtered, as such material can clog the filtering area. As a result, numerous techniques have been devised to aid in improving the filtration of liquids containing insoluble material. For example, one technique involves dispersing the insoluble material throughout the liquid prior to filtration in order to avoid clogging the filter area. While this approach may initially deter the insoluble material from collecting in the filter area, the material remains present in the liquid and eventually does settle into and clog the filter. Alternatively the insoluble material can actually be removed from the liquid before the filtration process begins. Usually this is achieved with a screen or other straining device, in essence, putting the liquid through an initial filtration. Another method subjects the liquid sample to centrifugation prior to filtration in order to remove the insoluble material. Here, the insoluble material is discarded and the fluid supernatant is filtered. Although techniques that involve the removal of the insoluble material prior to filtration are generally more effective, they do require additional manipulation of the liquid sample, increasing the amount of time spent on the procedure and raising the likelihood of error.
Insoluble materials are often not the sole barriers to successful, efficient filtration The above-described methods often fail to remove large particulate material from liquid samples, as well. Typical approaches for removing these large particulate materials often require sequential filtration processes. Generally, the insoluble or large particulate material is first precipitated via centrifugation. The remaining large unprecipitated particulate material is then removed with an initial filtration step involving a very coarse or porous filtering material. The filtered liquid is then subjected to further filtration as necessary. Again, this lengthens the duration of sample handling, and increases the possibility of error.
Often a liquid sample contains undesirable non-particulate material and several techniques have been devised to neutralize and remove these substances from the liquid sample either prior to or during filtration. While it is sometimes possible to neutralize undesirable non-particulate material by exposing the sample to ultraviolet light, heat, chemical substances, etc., this exposure may also neutralize substances in the sample that are desirable. As with the above-mentioned filtration methods, these techniques increase the number of manipulations necessary to filter the liquid and therefore make them more difficult and costly to perform. Special filtering material may be used as an alternative to the above-mentioned technique for removing undesirable non-particulate material from liquid samples, however, this filtering material often exhibits a limited capacity to remove, absorb and/or neutralize the undesirable non-particulate material. Additionally, this specialized filtering material is often not particularly suited for use in filtering liquids that contain more than one type of undesirable component.
While it is true that the majority of filtration techniques and devices are designed with the filtration of the entire volume of the liquid sample in mind, it is sometimes preferable to filter only a small portion of the total sample. Of those techniques that allow only a small portion of the liquid sample to be filtered, the volume of the resulting filtrate is often not related to the initial volume of the liquid. This may prove unsatisfactory when it is important that the filtrate volume relate directly to the initial volume of the liquid sample prior to being filtered.
For the foregoing reasons, it is clear that there exists a need for a filtration method, apparatus, and device that simply, accurately, effectively, and efficiently remove a wide variety of undesirable substances from a liquid sample in a manner that prevents the filtering area from becoming clogged with the precipitated insoluble and particulate material, without exceeding the filtering capacity of any of the filtering materials, to produce a volume of filtrate that is proportional to the initial volume of the liquid sample.